POLYMER NETWORKS BASED ON THE DIEPOXIDE DIISOCYANATE REACTION CATALYZED BY TERTIARY-AMINES

Reactions taking place in a system consisting of a diepoxide (DGEBA, d iglycidylether of bisphenol A) and a diisocyanate (TDI 80 : 20, toluen e diisocyanate), catalyzed by a tertiary amine (BDMA, benzyldimethylam ine), were followed by differential scanning calorimetry (DSC), infrar ed spectroscopy (FTIR), and chemical titration of isocyanate groups in the pre-gel stage. It was found that the main reactions took place in series, in steps of increasing temperature: (i) isocyanurate formatio n, (ii) epoxy-isocyanate reaction leading to oxazolidone rings, and (i ii) isocyanurate decomposition by epoxy groups producing oxazolidone r ings. Isocyanurate rings were stable in the presence of epoxides and a n isocyanate excess [reaction (ii) was faster than (iii)]. Epoxy hompo lymerization (secondary reaction) occurred in parallel with steps (ii) and (iii). Step (i) took place by two different mechanisms and led to a maximum conversion, possibly limited by topological restrictions. A kinetic study of TDI trimerization in the presence of an equimolar am ount of DGEBA and variable amounts of BDMA led to a third-order regres sion with an activation energy E = 43 kJ/mol. (C) 1995 John Wiley & So ns, Inc.